linux-kernel - [PATCH v1 04/13] kho: Verify deserialization status and fix FDT alignment access

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Message-ID: <20251114155358.2884014-5-pasha.tatashin@soleen.com>
Date: Fri, 14 Nov 2025 10:53:49 -0500
From: Pasha Tatashin <pasha.tatashin@...een.com>
To: akpm@...ux-foundation.org,
	bhe@...hat.com,
	pasha.tatashin@...een.com,
	rppt@...nel.org,
	jasonmiu@...gle.com,
	arnd@...db.de,
	coxu@...hat.com,
	dave@...ilevsky.ca,
	ebiggers@...gle.com,
	graf@...zon.com,
	kees@...nel.org,
	linux-kernel@...r.kernel.org,
	kexec@...ts.infradead.org,
	linux-mm@...ck.org
Subject: [PATCH v1 04/13] kho: Verify deserialization status and fix FDT alignment access

During boot, kho_restore_folio() relies on the memory map having been
successfully deserialized. If deserialization fails or no map is present,
attempting to restore the FDT folio is unsafe.

Update kho_mem_deserialize() to return a boolean indicating success. Use
this return value in kho_memory_init() to disable KHO if deserialization
fails. Also, the incoming FDT folio is never used, there is no reason to
restore it.

Additionally, use memcpy() to retrieve the memory map pointer from the FDT.
FDT properties are not guaranteed to be naturally aligned, and accessing
a 64-bit value via a pointer that is only 32-bit aligned can cause faults.

Signed-off-by: Pasha Tatashin <pasha.tatashin@...een.com>
---
 kernel/liveupdate/kexec_handover.c | 32 ++++++++++++++++++------------
 1 file changed, 19 insertions(+), 13 deletions(-)

diff --git a/kernel/liveupdate/kexec_handover.c b/kernel/liveupdate/kexec_handover.c
index a4b33ca79246..83aca3b4af15 100644
--- a/kernel/liveupdate/kexec_handover.c
+++ b/kernel/liveupdate/kexec_handover.c
@@ -450,20 +450,28 @@ static void __init deserialize_bitmap(unsigned int order,
 	}
 }
 
-static void __init kho_mem_deserialize(const void *fdt)
+/* Return true if memory was deserizlied */
+static bool __init kho_mem_deserialize(const void *fdt)
 {
 	struct khoser_mem_chunk *chunk;
-	const phys_addr_t *mem;
+	const void *mem_ptr;
+	u64 mem;
 	int len;
 
-	mem = fdt_getprop(fdt, 0, PROP_PRESERVED_MEMORY_MAP, &len);
-
-	if (!mem || len != sizeof(*mem)) {
+	mem_ptr = fdt_getprop(fdt, 0, PROP_PRESERVED_MEMORY_MAP, &len);
+	if (!mem_ptr || len != sizeof(u64)) {
 		pr_err("failed to get preserved memory bitmaps\n");
-		return;
+		return false;
 	}
+	/* FDT guarantees 32-bit alignment, have to use memcpy */
+	memcpy(&mem, mem_ptr, len);
+
+	chunk = mem ? phys_to_virt(mem) : NULL;
+
+	/* No preserved physical pages were passed, no deserialization */
+	if (!chunk)
+		return false;
 
-	chunk = *mem ? phys_to_virt(*mem) : NULL;
 	while (chunk) {
 		unsigned int i;
 
@@ -472,6 +480,8 @@ static void __init kho_mem_deserialize(const void *fdt)
 					   &chunk->bitmaps[i]);
 		chunk = KHOSER_LOAD_PTR(chunk->hdr.next);
 	}
+
+	return true;
 }
 
 /*
@@ -1377,16 +1387,12 @@ static void __init kho_release_scratch(void)
 
 void __init kho_memory_init(void)
 {
-	struct folio *folio;
-
 	if (kho_in.scratch_phys) {
 		kho_scratch = phys_to_virt(kho_in.scratch_phys);
 		kho_release_scratch();
 
-		kho_mem_deserialize(kho_get_fdt());
-		folio = kho_restore_folio(kho_in.fdt_phys);
-		if (!folio)
-			pr_warn("failed to restore folio for KHO fdt\n");
+		if (!kho_mem_deserialize(kho_get_fdt()))
+			kho_in.fdt_phys = 0;
 	} else {
 		kho_reserve_scratch();
 	}
-- 
2.52.0.rc1.455.g30608eb744-goog